Edge AI device to run inference
Since you said detection, you could do this on OpenCV: HAAR Cascade Detection for faces. It's swift, and should fit your use case. I've seen such scripts running on small Tello drones and gets job done relatively well.

Definitely there is hardware built around for this purpose. Look for Nvidia Jetson Nano and Jetson TK1/TX1. It's got sufficient juice to take even 30fps IMO.